It was not clear whether there were any casualties in the exchange of fire.

Turkey was angered by a US decision last month to arm the YPG as part of the battle for the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group's Syrian stronghold of Raqqa.

Ankara considers the YPG as an extension of the Kurdistan Workers Party (PKK), which is outlawed in Turkey and is also considered a "terrorist group" by the US and the European Union.

The PKK has carried out an armed uprising against the Turkish state since 1984 and more than 40,000 people, most of them Kurds, have died in the fighting.

Turkish dismay

Faced with turmoil across its southern border, Turkey last year sent troops into Syria to support Free Syrian Army rebels fighting both ISIL and Kurdish forces, who control a large part of Syria's northern border region.

Turkish President Recep Tayyip Erdogan has said that Turkey would not flinch from taking tougher action against the YPG in Syria if Turkey believed it needed to.

On Sunday, Erdogan said in a speech that countries that promised to get back weapons supplied to Kurdish YPG fighters in northern Syria were trying to trick Turkey and would eventually realise their mistake.

"But it will be too late for them," he added, saying that if violence spilled over Syria's border into Turkey, Ankara would hold to account anyone who supplied arms to the YPG.

"We will make the real owners of those weapons ... pay for any bullet that will be fired to our country, for every drop of blood that will be shed," he said.